The overall objectives of this project are to evaluate the ability of a simple clinical neurophysiological procedure based on the event-related potential(ERP) to distinguish dementia from depression and from the normal CNS changes associated with aging. We proposed to test the hypothesis that the latency of P300, a late positive component of the ERP associated with cognitive activity, will be greater in elderly patients suffering from dementia than in age and educationally matched patients suffering from depression. Our immediate goals are to recruit and clinically evaluate a population of elderly patients falling into three clinically distinct groups: (a) healthy elderly people with no evidence of neuropathology of psychopathology or depression, (b) patients who meet the DSM III criteria for senile dementia and presenile dementia but show no evidence of primary psychopathology, and (c) elderly people who meet the DSM III criteria for major depressive disorder but who show no evidence of dementia. Subjects participate in a one-hour test battery consisting of separate auditory and visual choice reaction time tasks designed to elicit analogous auditory and visual P300s. Resting EEG is also recorded for spectral analysis. CT scan data and Halsted-Reitan neuropsychological data are also obtained.